The present invention relates to a lamp unit which has particular utility for vehicle lamps. More particularly, the present invention relates to vehicle lamp units having an improved strap assembly for holding and supporting a light source within the vehicle lamp unit and also a method of clamping the light source to the improved strap assembly within a vehicle lamp.
Vehicle lamps such as sealed beam headlamp units are well-known and are disclosed in U.S. patent application Ser. No. 504,202 of B. E. Shanks, filed June 14, 1983 now abandoned and U.S. patent application Ser. No. 546,011 of R. F. Malinowski filed Oct. 27, 1983, now U.S. Pat No. 4,509,107 both of which are assigned to the same assignee as the present invention. The sealed beam headlamp of Shanks has a filament assembly which serves as a light source. The light source is internally arranged and predeterminedly located at a desired optical position within the unit. The filament is connected across ferrules, which, in turn, are connected to mating contact plugs or electrical terminals. The electrical terminals are connected to suitable electrical connectors, within the automobile, through which the filament is selectively energized in accordance with the switching devices within the automobile.
Vehicle lamps when placed within their intended environment encounter actual on-the-road use which subject the vehicle lamp to the vibrations of the engine of the vehicle and also to vibrations due to the tire interaction with the road surface being transmitted through the suspension system of the vehicle to the lamp unit. Further, vehicle lamps in their intended environment may also be subjected to substantial shock effects. The operating environment of the vehicle lamp may typically be manifested in forces which stress the metal parts of the vehicle lamp, more particularly, force which stress the metal parts of the support members supporting the light source of the lamp unit. The metal support members holding the light source within the lamp unit typically experience metal fatigue, which, in turn, ultimately results in a failure of the light source. The light source failure may be manifested in an open condition of the filament serving as the light source, or in movement of the light source with the lamp unit which in either case renders the vehicle lamp unfit for its intended use.
The failure of the light source due to the operating vibrations of the vehicle may be substantially reduced by strengthening the mounting arrangement of the light source within the lamp unit. The mounting arrangement may be stiffened so as to reduce the flexure induced by specific vibration frequencies of the vehicle typically in a range of about 50 Hz to about 500 Hz and by specific shock effects in the range of about 10 g's to about 20 g's. The mounting arrangement of the light source within the unit may be stiffened such that the frequency at which the mounting arrangement resonates may be raised above that previously discussed typical operating range experienced by the motor vehicle.
The stiffening of the light source mounting arrangement may be accomplished by increasing the dimensions of the support elements thereof. One manner to accomplish such an increase is to increase the dimensions of the external leads of the light source that interconnect the filament to external devices. If the light source is of a halogen type, the external leads are commonly embedded, sealed and brought out through the base of the halogen lamp having a sealed exhaust tip. The extent of the increased dimensions of the external leads should take into account the strength of the supporting glass in which the external lead wires are embedded. Increasing the external lead wire diameter commonly decreases the amount of supporting glass of the lamp and ultimately the thinner glass becomes the failure of fracture point of the halogen lamp when subjected to the vehicle vibrations. Further, reliance on external leads to provide for increased stiffening of light source mounting has a further disadvantage in that external lead wires may be somewhat embrittled by assembly or sealing operations related to the glass halogen type lamp. It is desired that the strengthening of the light source mounting be accomplished without relying upon an increase in the external lead wire diameter.
The increased support may also be accomplished by a strap assembly connected to a support member and placed around the halogen light source. The strap assembly should take into account the glass geometry in which it is mated and frictionally engages the glass envelope of the halogen light source. Frictional engagement should not overstress the glass so as to result in a fracture when the engagement is too tight or causes the glass to be placed in a tension condition ultimately resulting in glass fracture. Overstress of the glass is particularly noted if tensile type stresses result from the frictional engagement of the strap assembly to the glass envelope. It is desired that the frictional engagement only exert compressive forces onto the glass envelope which forces are less prone to cause glass fracture. Such a strap arrangement conforming to the glass geometry of the halogen light source may require by its very nature careful hand fitting and welding operations particularly if the strap assembly is mated to the base of the halogen light source having an irregular shape caused by the sealing and venting operation at the exhaust tip of the base. These careful operations typically result in an increase to the final cost of the vehicle lamp unit. It is desired that a strap assembly be mated to the glass geometry without encountering the previously discussed disadvantages.
The mounting arrangement may also be strengthened by potting methods that apply silicone adhesives or ceramic compositions to the light source mounting arrangement. These methods while increasing the support of the light source are relatively expensive and typically require a relatively long time for the silicone adhesive or ceramic compositions to cure and adhere to the light source. In the case of the ceramics a further disadvantage is encountered in that the ceramics may damage the glass surface to which they adhere. In the case of silicone adhesives, a further disadvantage is encountered in that the adhesion of these compositions is not generally capable of withstanding bulb temperature. Further, a disadvantage related to both the silicone and ceramic compositions is that the additional mass added by these compositions may adversely affect the vibration strength of the support member.
Accordingly, it is an object of the present invention to provide an improved support arrangement of a light source within a vehicle lamp that is not limited to the disadvantages of the prior known methods and allows the support arrangement to be easily connected to a halogen light source having an irregular shape particularly noted at its base.
It is a further object of the present invention to provide an improved supporting arrangement of a light source that only exerts compressive forces onto the halogen light source which are less prone to cause glass fracture when compared to tensile type stresses onto the halogen light source.
Still further, it is an object of the present invention to provide an improved light source support arrangement that does not require or even depend on the support of the external leads of the lamp unit.
Further still, it is an object of the present invention to provide a vehicle lamp unit that withstands the vibration and shock conditions encountered in a vehicle environment without experiencing a light source failure.